Validation of Compressibility Test Systems for Friction Materials
This SAE Recommended Practice applies to the validation process required for test systems used to measure deflection or compressibility of friction materials and friction material assemblies for passenger cars, light trucks, and commercial vehicles equipped with hydraulic or air brake systems, and using disc or drum brakes.
Rationale: Within any acceptable Quality Assurance program, the systematic verification of the test system and Gage Repeatability and Reproducibility (Gage r&R) are of primary importance. Manufacturing or Product Data is only as good as the instruments that evaluate the processes or measure the physical products. Therefore, it is of primary importance to ensure that measurement devices are adequate and appropriate as part of the product development, and the manufacturing control plan. More so, since compressibility test results are one of the most exchanged in the friction material supply chain.
This recommended practice uses three main steps:
a. Assessment of test system using a predefined checklist to verify main features and control capabilities with deflection profile evaluations
b. Measurement of actual deflection using standard proving rings (also known as standard judge and soft judge)
c. Gage r&R using actual brake pad assemblies following a pre-selection process
Using test systems which satisfy the statistical limits and acceptance criteria established in this RP in addition to any agreed upon requirements between the testing system supplier and the test system user, provides a robust method to ensure valid and relevant test results.
This RP accompanies and supports the SAE Surface Vehicle Standards:
• SAE J2468 – High-preload Deflection and Compressibility Test Procedures for Friction Materials
• SAE J3079-2 – Low-preload Deflection Measurement for Brake Pads, Noise Shims, and Brake Pad Assemblies